1. Field of the Invention
The present invention relates generally to a photographing method and apparatus, and more particularly to a photographing method and apparatus for photographing a fluorescent image of the fluorescent light emitted by a subject and a reflected light-image, etc. of a subject illuminated by a faint light.
2. Description of the Related Art
There has been expressed a desire for photographing a fluorescent image of the fluorescent light emitted by a subject and a reflected-light image of a subject illuminated by a faint light as clear images, and much discussion has ensued in regard to development of a high-sensitivity photographing system therefor.
For example, research has been conducted on an apparatus which, by analyzing fluorescent light-images obtained by photographing the fluorescent light emitted by the inherent dye of the structures of a living tissue illuminated by a stimulating light, facilitates the distinguishing of changes, etc. in the state of each type of disease. In a fluorescent endoscope, the image of the fluorescent light emitted by a subject is propagated along an image fiber and guided to the end thereof. The size of the image guided into the image fiber is magnified to a larger size than that at which it entered the image fiber, focused on a photographing element and photographed.
The fluorescent light emitted by the structures of a living tissue is faint, and a high-sensitivity photographing element is used to detect this light as an image. When the quantity of light received by the photographing element is large, the fluorescent image is photographed at the resolution corresponding to the number of pixels provided on the photographing element, however, when the quantity of light received by the photographing element is small, the signal charge of a plurality of pixels is multiplied, readout, subjected to a pixel binning processing, and the fluorescent image is photographed. For example, if an image fiber of a 2 mm diameter is constituted of 10,000 strands and the image formed by fluorescent light at the end of this fiber is formed of 10,000 pixels, the light-receiving zone of the photographing element for receiving this image is provided with 4 times the number of pixels (40,000 pixels or more). When, for example, the phosphor image received uses 25,000 or 38,000, etc. substantially all of the light-receiving zone of the photographing element, and when the quantity of fluorescent light received is small, the number of pixels to be subjected to pixel binning processing; that is, the number of pixels corresponding to 1 pixel is multiplied and increased, the quantity of light received corresponding to one pixel is increased and the resolution decreased, and conversely, when the quantity of fluorescent light received is large, the number of pixels to be subjected to pixel binning processing is reduced, the resolution increased and the image photographed.
More specifically, a desire has been expressed to obtain an image of a cancerous portion, which is located 50 mm away from the point on which the stimulated light is emitted, as an image signal having a S/N ratio of 1 or higher under standard photographing conditions, in which the structures of a living tissue are illuminated by a 120xc2x0 wide, 100 mw stimulating light and exposed for {fraction (1/30)} of a second over the entire light-receiving zone.
When photographing is performed using a front-exposure type photographing element under aforementioned standard photographing conditions, because the normal charge of the image signal representing the fluorescent image of aforementioned cancerous portion stored on 1 pixel of the light-receiving zone is substantially 10 electrons, by controlling the sum of the number of electrons of the readout noise of each pixel of the light-receiving zone and the number of electrons of dark noise to 10 electrons or less, a S/N ratio of 1 or higher can be obtained for the image signal representing the fluorescent light-image of the cancerous portion. In addition, for cases in which a rear-exposure type photographing element, which has a quantum efficiency substantially twice that of aforementioned front-exposure photographing element, is used, because the charge of the image signal representing the fluorescent image stored on 1 pixel under the settings of aforementioned standard photographing conditions is substantially 20 electrons, by controlling the sum of the number of electrons of the readout noise of each pixel of the light-receiving zone and the number of electrons of dark noise to 20 electrons or less, a S/N ratio of 1 or higher can be obtained for the image signal representing the fluorescent light-image of the cancerous tissue.
However, even if the above described method of employing a processing such as pixel binning is used, when the signal charge that has been stored on a plurality of pixels receiving the fluorescent light the fluorescent image is multiplied within the photographing element, because the signal charge generated due to reception of fluorescent light is in the end simultaneously multiplied together with the signal charge stored due to the dark noise, even if the charge of the image signal stored on a plurality of pixels is grouped together as a unit by being subjected to pixel binning processing and are and treated as corresponding to 1 pixel, the ratio of the dark noise component is not reduced, and an improvement in the S/N ratio cannot be hoped for. At this point, a photographing system in which the S/N ratio can be improved by reducing the dark noise component is desired.
The present invention has been developed in consideration of the circumstances described above, and it is a primary object of the present invention to provide a faint light photographing method and apparatus in which, by reducing the dark noise, the light-image of a subject can be photographed as an image having a high S/N ratio.
According to the photographing method of the present invention, in which fluorescent light emitted by a living-tissue subject illuminated by stimulating light enters an image fiber and is guided toward the output face of the image fiber, and the fluorescent image formed at the output face of the image fiber is focused on the light-receiving zone of the photographing element and photographed by the photographing element, the relationship between the number of pixels Nf forming the fluorescent image on the output face of the image fiber and the number of pixels Nd receiving the light of the fluorescent image assembled within the light-receiving zone of the photographing element satisfy the condition expressed by the formula: Nfxc3x974 greater than Nd.
For cases in which a front-exposure type photographing element is used, at normal temperature or lower, it is preferable that the fluorescent image be photographed under photographing conditions set so that the sum of the number of electrons of the readout noise produced on each pixel within the light-receiving zone receiving the light of a fluorescent image and the number of electrons of dark noise be 10 or less.
For cases in which a rear-exposure type photographing element is used, at normal temperature or lower, it is preferable that the fluorescent image be photographed with the photographing conditions set so that the sum of the number of electrons of the readout noise produced on each pixel within the light-receiving zone receiving the light of a fluorescent image and of dark noise be 20 or less.
It is preferable that the fluorescent image be focused on an imaged focusing means in which the number of pixels of the light-receiving zone receiving the light of the fluorescent image is 40,000 or less.
For cases in which the photographing element is capable of reading out, in a random manner, the signal charge stored on each pixel, it is preferable that a readout zone narrower than the light-receiving zone and which includes the fluorescent image is set within the light-receiving zone, and that readout of the readout zone be performed prior to readout of other zones within the light-receiving zone.
For cases in which the photographing element reads out the signal charge stored on each pixel sequentially, it is preferable that the fluorescent image be assembled at the closest position to the readout port of the photographing element, within the light-receiving zone.
A photographing apparatus according to the present invention comprises an optical system for directing fluorescent light emitted from a living-tissue subject illuminated by stimulating light into an image fiber and guiding it to the output face of the image fiber, an image focusing means for focusing on the light-receiving zone of the photographing element the fluorescent image formed by the fluorescent light guided to the output face of the image fiber, and a photographing means for photographing the fluorescent image assembled at the light-receiving zone thereof, wherein the relationship between the number of pixels Nf forming the fluorescent image on the output face of the image fiber and the number of pixels Nd receiving light of the fluorescent image assembled within the light-receiving zone of the photographing element satisfy the condition expressed by the formula: Nfxc3x974 greater than Nd.
For cases in which the photographing element of the photographing means is provided as a front-exposure type photographing element, at normal temperature or lower, it is preferable that the fluorescent image be photographed under photographing conditions set so that the sum of the number of electrons of the readout noise produced on each pixel within the light-receiving zone receiving the light of a fluorescent image and the number of electrons of dark noise be 10 or less.
For cases in which the photographing element of the photographing means is provided as a rear-exposure type photographing element, at normal temperature or lower, it is preferable that the fluorescent image be photographed under photographing conditions set so that the sum of the number of electrons of the readout noise produced on each pixel within the light-receiving zone receiving the light of a fluorescent image and the number of electrons of dark noise be 20 or less.
It is preferable that the fluorescent image be focused on an imaged focusing means in which the number of pixels of the light-receiving zone receiving the light of the fluorescent image is 40,000 or less.
The image focusing means can be a means capable of changing, corresponding to the quantity of fluorescent light received by the photographing element, the size of the fluorescent image assembled within the light-receiving zone thereof.
The image focusing means is provided with a zooming optical system, and by use of the zooming optical system, can be a means capable of changing the size of the fluorescent image assembled within the light-receiving zone thereof.
The photographing apparatus can also be a photographing element that changes the readout frequency of the photographing element, corresponding to the zooming rate of the zooming optical system.
For cases in which the photographing element is capable of reading out in a random manner the image signal charge stored on each pixel, it is preferable that the photographing means be provided with a readout control means for setting a readout zone narrower than the light-receiving zone and which includes the fluorescent image within the light-receiving zone, and causing readout of the readout zone to be performed prior to readout of other zones within the light-receiving zone.
For cases in which the photographing element is capable of reading out in a random manner the image signal charge stored on each pixel, it is preferable that the photographing means be provided with a readout control means for setting a readout zone narrower than the light-receiving zone and which includes the fluorescent image within the light-receiving zone, which is also capable of changing the size of the readout zone and causing readout of the readout zone to be performed before readout of other zones within the light-receiving zone.
For cases in which the photographing element is a photographing element that sequentially reads out the image signal charge stored on each pixel, it is preferable that the photographing element is structured so that the fluorescent image is assembled at the closest position to the readout port of the photographing element, within the light-receiving zone.
For cases in which the photographing element is a photographing element that sequentially reads out the image signal charge stored on each pixel, it is preferable that the photographing element be provided with an focusing-position changing means for changing the position at which the fluorescent image is assembled within the light-receiving zone.
According to a photographing method of the present invention: a photographing element in which the charge stored on each pixel is sequentially transferred and readout is utilized; the light-image of the subject is focused on the light-receiving zone of the photographing element; the assembled light-image is photoelectrically converted on each light-receiving pixel within the light-receiving zone and stored within each light-receiving pixel as an image charge; and the signal charge stored within each light-receiving pixel is converted to an image signal and readout. In addition, the light-image is focused on the light-receiving pixels of a readout zone formed from less than the total number of pixels of the light-receiving zone, and the readout signal charge transferred to and stored on the light-receiving pixels contained within the readout zone is readout as aforementioned image charge and the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone is readout as a null change.
According to aforementioned photographing method, the sequentially transferred readout signal charge can be subjected to binning processing before it is readout.
According to another photographing method of the present invention: a photographing element in which the charge stored on each pixel is sequentially transferred and readout is utilized; the light-image of the subject is focused on the light-receiving zone of the photographing element; the assembled light-image is photoelectrically converted on each light-receiving pixel within the light-receiving zone and stored within each light-receiving pixel as an image charge; and the signal charge stored within each light-receiving pixel is converted to an image signal and readout. In addition, the light-image is focused on the light-receiving pixels of a readout zone formed from less than the total number of pixels of the light-receiving zone, and the readout signal charge transferred to and stored on the light-receiving pixels contained within the readout zone is readout as aforementioned image charge and the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone is discarded through a clearing drain.
According to a further photographing method of the present invention: a photographing element in which the charge stored on each pixel is sequentially transferred and readout is utilized; in which the light-image of the subject is focused on the light-receiving zone of the photographing element; the assembled light-image is photoelectrically converted on each light-receiving pixel within the light-receiving zone and stored within each light-receiving pixel as an image charge; and the signal charge stored within each light-receiving pixel is converted to an electric image signal and readout. In addition, the light-image is focused on the light-receiving pixels of a readout zone formed from less than the total number of pixels of the light-receiving zone, and after the readout signal charge transferred to and stored on the light-receiving pixels contained within the readout zone is readout as aforementioned image charge, the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone, or aforementioned residual signal charge and the image signal charge stored on the light-receiving pixels contained within the light-receiving zone after the readout signal charge has been read out are grouped together and read out as null for each block or one pixel at a time.
A photographing apparatus according to the present invention comprises a photographing element and an image focusing means for focusing the light-image of a subject in the light-receiving zone of the photographing element. The photographing element is provided with a photoelectric converting portion for photoelectrically converting and accumulating as an image signal the received light on each light-receiving pixel within the light-receiving zone, a charge transfer portion for sequentially transferring the image charge stored on each light-receiving pixel, and a sequential-readout portion for converting the sequentially transferred image charge to an electric image signal and reading out said image charge, wherein said image focusing means focuses the light-image on the light-receiving pixels of a readout zone formed from less than the total number of pixels of the light-receiving zone, and a sequential-readout control means is provided for controlling the readout as an image signal of the readout charge stored on the light-receiving pixels of the readout zone by the sequential-readout portion and the readout as null of the residual signal charge stored on the light-receiving pixels outside the readout zone in the non-readout zone by the sequential-readout portion.
Aforementioned photographing apparatus can be provided with a gate between the charge transfer portion and the sequential-readout portion for controlling passage of the signal charge from the charge transfer portion to the sequential-readout portion, and a gate control means for controlling aforementioned gate so as to facilitate the subjecting of said readout signal charge to binning processing before the readout signal charge is transferred by the charge conversion portion and read out by the sequential-readout portion.
A further photographing apparatus according to the present invention comprises a photographing element and an image focusing means for focusing the light-image of the subject in the light-receiving zone of the photographing element, and the photographing element is provided with a photoelectric converting portion for photoelectrically converting and storing as an image signal the received light on each light-receiving pixel within the light-receiving zone, a charge transfer portion for sequentially transferring the image charge stored on each light-receiving pixel, and a sequential-readout portion for converting the sequentially transferred image charge to an electric image signal and reading out said image charge, wherein said image focusing means focuses the light-image on the light-receiving pixels of a readout zone formed from less than the total number of pixels of the light-receiving zone, and is further provided with a clearing drain for discarding the signal charge sequentially transferred by the charge transfer portion, and a sequential-readout control means for controlling readout of the readout signal charge, which is stored on the light-receiving pixels of the readout zone, by the sequential readout means and the discarding of the residual signal charge, which is stored on the light-receiving pixels outside the readout zone in the non-readout zone, into the clearing drain.
A still further photographing apparatus of the present invention comprises a first gate provided between the charge transfer portion and the sequential-readout portion for controlling passage of the signal charge from the charge transfer portion to the sequential-readout portion, a second gate provided between the charge transfer portion and aforementioned clearing drain for controlling passage of the signal charge from the charge transfer portion to the clearing drain, and a gate control means for controlling gate 1 and gate 2 so as to facilitate the subjecting of the readout signal charge to binning processing before the readout signal charge is transferred by said charge conversion portion and read out by the sequential-readout portion.
Yet another photographing apparatus of the present invention comprises a photographing element and an image focusing means for focusing the light-image of the subject in the light-receiving zone of the photographing element, and the photographing element is provided with a photoelectric converting portion for photoelectrically converting and accumulating as an image signal the light received on each light-receiving pixel within the light-receiving zone, a pixel selecting means capable of randomly selecting pixels from among the light-receiving pixels, and a random readout portion for photoelectrically converting the signal charge of the selected light-receiving pixels to an electric image signal and reading it out, wherein the image focusing means focuses the light-image on the light-receiving pixels of a readout zone formed from less than total number of pixels of the light-receiving zone, and the pixel selecting portion selects light-receiving pixels of the readout zone, and after the random readout portion reads out the image charge stored on the selected light-receiving pixels, the pixel selecting means selects light-receiving pixels contained in the non-readout zone outside the readout zone, or the pixels contained in the non-readout zone and the readout zone, and a random readout control means is provided to control the pixel selecting portion and the random readout portion so as to facilitate readout as a null change for each block or one pixel at a time by the random readout means of the residual signal charge stored on the light-receiving pixels in the non-readout zone or aforementioned residual signal charge grouped together with the image signal charge stored on the light-receiving pixels contained within the light-receiving zone.
According to the random readout control means, at the same time a plurality of light-receiving pixels within the light-receiving zone are selected by the pixel selecting means, binning processing can be performed on the readout signal charge so that the multiplied signal charge of each readout signal charge stored on the selected light-receiving pixels can be converted to an electric image signal and readout.
According to aforementioned photographing apparatus, the image focusing means is provided with a zooming optical system, and said zooming optical system can be a means capable of changing the size of the light image focused on the light-receiving zone.
The photographing apparatus can also be a photographing element that changes the readout frequency of the photographing element, corresponding to the zooming rate of the zooming optical system.
Aforementioned photographing apparatus can be loaded in a fluorescent endoscope.
According to the photographing method and apparatus described above, the photographing element can be a charge amplification type for amplifying the charge by impact ionization.
Note that the xe2x80x9ccharge-amplification type photographing elementxe2x80x9d for amplifying the charge by impact ionization is a photographing element having a shift-resistor provided with a charge amplifying function and which is disposed between the horizontal CCD readout shift-resistor and the output amplifier. The operating principle by which the shift-resistor provided with a charge amplifying function amplifies the charge is the impact ionization phenomenon, which forms 2-dimensional electrons, occurring when the signal charge is transferred in deep potential formed at a sufficient strength (the charge collides with Si, and electron holes are formed). By transferring the signal charge, which has been transferred from the horizontal readout shift-resistor, by the multi-step shift-resistors of the shift-resistor provided with a charge amplifying function, each having deep potential, the 2-dimensional electrons are repeatedly formed, the readout noise level is not substantially increased and the signal charge is amplified. In relation to this charge-amplification type photographing element for amplifying a charge by use of impact ionization, refer to the specification of U.S. Pat. No. 5,337,340 (name of invention: Charge Multiplying Detector  less than CMD greater than  suitable for small pixel CCD image sensor).
According to the photographing method and apparatus of the present invention, in photographing of a fluorescent image focused on the light-receiving zone of the photographing element, because the fluorescent image is focused on the light-receiving zone wherein the relationship of the pixels Nf, which represent the fluorescent image formed on the output face of the image fiber, to the pixels Nd, which are the pixels in the light-receiving zone receiving the light of the fluorescent image assembled therein, satisfies the condition expressed by the formula: Nfxc3x974 greater than Nd. That is, because the number of pixels of the light-receiving zone of the photographing element focusing the fluorescent image formed at the output face of the image fiber has been kept not unnecessarily high, the quantity of dark noise produced per each pixel is not changed and quantity of fluorescent light received per pixel is increased, and because the fluorescent image, having a relatively reduced ratio of dark noise, can be read out from the photographing element, the fluorescent image can be photographed as an image having a high S/N ratio.
Note that for cases in which a front-exposure type photographing element is used, if the photographing conditions are set so that the sum of the number of noise and dark noise electrons produced on each pixel in the light-receiving zone receiving the light of the fluorescent image, at normal temperature or lower, is 10 or less, in aforementioned standard photographing state, an image of a cancerous tissue, for example, can be photographed having an S/N ratio of 1 or higher.
In addition, for cases in which a rear-exposure type photographing element is used, if the photographing conditions are set so that the sum of the number of noise and dark noise electrons produced on each pixel in the light-receiving zone receiving the light of the fluorescent image at normal temperature or lower is 20 or less, because the quantum efficiency of a rear-exposure photographing element becomes twice that of a front-exposure photographing element, in aforementioned standard photographing state, an image of a cancerous tissue, for example, can be photographed having an S/N ratio of 1 or higher.
Further, if the fluorescent image is assembled and photographed in a light-receiving zone in which and the number of pixels receiving the light of the fluorescent image is 40,000 or less, even for cases, for example, in which there are sufficiently plentiful pixels to represent the image formed at the output face of the image fiber, there are not an excess number of unnecessary pixels receiving the light of the fluorescent image in the light-receiving zone, and by controlling the number of pixels receiving the light of the fluorescent image to 40,000 or less, which is a number of pixels providing for the capability for distinguishing the change, etc. in the state of diseased tissues of various diseases by analyzing the photographed fluorescent image, a fluorescent image in which the quantity of light received per pixel is further increased can be read out from the photographing element, and the fluorescent image can be photographed as an image with a higher S/N ratio.
Further yet, if the size of the fluorescent image focused on the photographing element is changed, corresponding to the amount of light received at the photographing element, by use of a zooming optical means, etc., in a case, for example, when the quantity of received light of the fluorescent image is small, the fluorescent image is assembled small on the photographing element, and by photographing the fluorescent image by use of few pixels, the quantity of light received per pixel increases and the resolution of the image deteriorates, and for cases in which the quantity of received light of the fluorescent image is large, the fluorescent image assembled large on the photographing element, and by photographing the fluorescent image by use of many pixels, because adjustment can be made so that the quantity of received light is ensured while increasing the resolution, the fluorescent image can be photographed as an image having both the appropriate quantity of received-light and resolution.
Still further, if the photographing element is provided so that it is capable of reading out, in a random manner, the image charge stored on each pixel and with a readout zone including the fluorescent image and narrower than the light-receiving zone, if readout of the readout zone is performed prior to readout of the other zones, the time for dark noise to accumulate on each pixel of the readout zone, which are read out before the pixels of the other zones, can be shortened, and the fluorescent image can be read out as an image having a high S/N ratio.
Further still, if the photographing element is provided so as to sequentially read out the signal charge stored on each pixel and assemble the fluorescent image at the point closest to the readout port of the photographing element within the light-receiving zone thereof, compared to other cases, because the light of the fluorescent image received at each pixel is read out faster and the time for dark noise to accumulate can be reduced, the fluorescent image can be photographed as an image having a higher S/N ratio.
In addition, if the photographing element is provided so that it is capable of reading out, in a random manner, the signal charge stored on each pixel, and a readout zone, which is read out prior to other zones and whose size it is possible to change, is set within the light-receiving zone of the photographing element, in a case, for example, in which the size of an image to be assembled is changed corresponding to the quantity of received light, the position at which the fluorescent image is to be assembled can be set close to aforementioned readout port corresponding to the change in size thereof, by which efficient early readout of the fluorescent image becomes possible, and the fluorescent image can be photographed as an image having a higher S/N ratio.
Further, if the photographic element is provided so that it sequentially reads out the signal charge stored on each pixel, and so that it is possible to change the position at which the fluorescent image is assembled within the light-receiving zone thereof, in a case, for example, in which the size of an image to be assembled is changed corresponding to the quantity of received light, the position at which the fluorescent image is to be assembled can be set close to aforementioned readout port corresponding to the change in size thereof, by which efficient early readout of the fluorescent image becomes possible, and the fluorescent image can be photographed as an image having a higher S/N ratio.
According to a photographing method and apparatus of the present invention, a photographing element for sequentially transferring and reading out the signal charge stored on each pixel is utilized, and in converting the signal charge stored in each pixel to an electric image signal and reading out said image signal, the light-image is focused on the light-receiving pixels of a readout zone formed from less than the total number of pixels of the light-receiving zone, and accompanying the conversion and readout of the readout signal charge, which has been transferred to and stored on the light-receiving pixels contained within the readout zone, as an image charge, because the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone has been read out as null, the quantity of dark noise produced per each pixel is not changed and quantity of fluorescent light received per pixel can be increased twofold or greater, and because the ratio of dark noise of the fluorescent image can be relatively reduced, the fluorescent image can be photographed as an image having a high S/N ratio.
Note that upon converting the signal charge stored on each light receiving pixel image signal charge and reading out said image signal, the light-image of the subject is focused in a readout zone formed of a number of light-receiving pixels equal to less than half of the total number of light-receiving pixels of the light-receiving zone. Accompanying the conversion to an image signal of the readout signal charge that has been transferred to the readout zone and readout of said image signal, if the residual signal charge that has been transferred to and stored on the light-receiving pixels of the no-readout zone outside of the readout zone is read out as a null change, because the quantity of dark noise produced per pixel does not change and the quantity of light received per pixel can be increased by more than double and the ratio of dark noise can be relatively reduced, the light-image can be photographed as an image having a higher S/N ratio.
According to another photographing method and apparatus of the present invention, a photographing element for sequentially transferring and reading out the signal charge stored on each pixel is utilized, and in converting the signal charge stored in each pixel to an electric image signal and reading out said image signal, the light-image is focused on the light-receiving pixels of a readout zone formed from less than less of the total number of pixels of the light-receiving zone, and accompanying the conversion of the readout signal charge transferred to and stored on the light-receiving pixels contained within the readout zone to an image signal and readout of said image signal, because the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone has been discarded via a clearing drain, the quantity of dark noise produced per each pixel is not changed and quantity of fluorescent light received per pixel can be increased twofold or greater the quantity of dark noise produced per each pixel is not changed and quantity of fluorescent light received per pixel can be increased twofold or greater, the ratio of dark noise of the fluorescent image can be relatively reduced, and it is not necessary to convert the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone to an image signal and read out and discard the thus converted image signal as in the prior art, and because the residual signal charge transferred to and stored on the light-receiving pixels outside the readout zone in the non-readout zone has been discarded at a high speed via the clearing drain, the processing time for one section of the display is shortened, and readout of the signal charge stored in the readout zone can be completed rapidly, the quantity of dark noise can be further reduced with the passage of time and the fluorescent image can be photographed as an image having a high S/N ratio.
Note that upon converting the signal charge stored on each light receiving pixel image signal charge and reading out said image signal, the fluorescent image o the subject is focused in a readout zone formed of a number of light-receiving pixels equal to less than half of the total number of light-receiving pixels of the light-receiving zone. Accompanying the conversion to an image signal of the readout signal charge that has been transferred to the readout zone and readout of said image signal, if the residual signal charge that has been transferred to and stored on the light-receiving pixels of the no-readout zone outside of the readout zone is discarded via a clearing drain, the quantity of dark noise produced per pixel does not change, and by increasing the quantity of light received per pixel by more that double, the ratio of dark noise can be relatively reduced, and because the residual signal charge stored on the light-receiving pixels of the non-readout zone outside the readout zone is not converted to an image signal and readout and discarded as in conventional processing, but is discarded via a clearing drain at a high speed, readout of the signal charge of the readout zone can be completed rapidly, an because the quantity of dark noise, which accumulates with the passage of time, can be further reduced, the light image can be photographed as an image having a higher S/N ratio.
According to yet another photographing method and apparatus of the present invention, a photographing element for sequentially transferring and reading out the signal charge stored on each pixel is utilized, and in converting the signal charge stored in each pixel to an electric image signal and reading out said image signal, the light-image is focused on the light-receiving pixels forming the readout zone, which account for xc2xd or less of the total number of pixels of the light-receiving zone, and after readout of the readout signal charge stored on the light-receiving pixels contained within the readout zone as an image signal, because the residual signal charge stored on the light-receiving pixels contained in the non-readout zone outside the readout zone, or said residual signal charge together with the signal charge stored on the light-receiving pixels contained in said readout zone after readout of the readout signal charge have been read out from said random readout portion as null for each block or one pixel at a time, readout of the signal charge stored on the light-receiving pixels in the readout zone can be completed more rapidly and the quantity of dark noise, which accumulates with the passage of time, can be further reduced. Also, the blooming that occurs in cases in which the residual signal charge stored on the light-receiving pixels of the non-readout zone is not discarded, that is, the phenomenon wherein a signal charge continues to accumulate on the light-receiving pixels of the non-readout zone and overflows onto the light-receiving pixels of the readout zone can be prevented.
According to a still further readout method and apparatus of the present invention, employing a photographing element capable of reading out, in a random manner, the signal charge stored on each light-receiving pixel, upon conversion of the signal charge stored on each light-receiving pixel to an electric image signal and readout of said image signal, the light-image of the subject is focused in a readout zone formed of a number of light-receiving pixels equal to less than half of the total number of light-receiving pixels of the light-receiving zone, and after readout of the readout signal charge, as an image signal, stored on each of the light-receiving pixels of said readout zone, if the residual signal charge stored on the light-receiving pixels of the non-readout zone outside the readout zone, or said residual signal charge grouped together with the signal charge stored on the readout zone after the readout signal charge has been readout therefrom is readout as empty for each block or each pixel, readout of the signal charge stored on the light-receiving pixels of the readout zone can be completed more rapidly, and the quantity of dark noise, which accumulates with the passage of time, can be reduced. Further, the blooming occurring for cases in which discarding of the residual signal charge stored on the light-receiving pixels of the non-readout zone has not been performed, that is, the phenomenon wherein the signal charge continuing to be accumulated on the light-receiving pixels of the non-readout zone overflows onto the light-receiving pixels within the readout zone, can be prevented.
Further, if aforementioned readout signal charge is subjected to binning processing, because the signal charge stored on a plurality of pixels can be grouped together as a unit and converted to an image signal, the readout noise produced when a signal charge is converted to an electric image signal can be further reduced and image signal carrying the light-image of a subject can be photographed as an image having an even higher S/N ratio.
Still further, if the image focusing means is provided with a zooming optical means, by use of which it becomes a means capable of changing the size of the light-image to be focused on the light-receiving zone, for cases in which the quantity of light received from the light-image is insufficient and an image signal having a low S/N ratio is read out, by focusing the light image in a small area within the light-receiving zone, the quantity of light received per pixel is increased and the light-image can be read out as an image signal having a high S/N ratio. In addition, for cases in which the quantity of light received from the light-image is sufficiently large and an image signal having a high S/N ratio has been read out, by focusing the light-image on a larger area of the light-receiving zone, the number of light-receiving pixels receiving the light of the light-image is increased, and an image signal carrying a light-image having a higher resolution can be read out.
In addition, if the photographing apparatus is a photographing element that changes the readout frequency, corresponding to the zooming rate of the zooming optical system, the level of readout noise mixed in the images to be readout can be more precisely made to be low. That is to say, for cases in which a normal photographing element is used, because the quantity of readout noise produced is proportional to the horizontal base of the readout frequency, if the readout frequency is lowered, the quantity of readout noise can be caused to be low. For example, if the zooming rate of the zooming optical system is set low, and a predetermined observation zone is focused smaller on the photographing element and the number of readout pixels reduced, the readout frequency can be lowered by only the portion of the number of pixels read out for 1 frame and the quantity of readout noise produced can be precisely made to be small.
More specifically, for example, in a case in which a normal photographing element is employed under a photographing condition of 30 frames/second, the readout noise is more controlled than the dark noise, and reducing the readout noise becomes a means of improving the sensitivity (improving the S/N ratio). Because the quantity of readout noise produced is proportional to the horizontal base of the readout frequency, if the readout frequency is lowered, it is possible to raise the sensitivity (S/N). Here, if the predetermined observation zone is focused smaller on the photographing element by the zooming optical means and the number of pixels read out is reduced, the readout frequency can be lowered by only the portion of the number of pixels read out for 1 frame and the quantity of readout noise produced can be precisely made to be small. If the readout frequency becomes low, the quantity of readout noise produced is reduced, and the sensitivity (S/N) can be improved.
If the photographing apparatus is implemented in an endoscope apparatus, because the quantity of light received per pixel is increased and the dark noise can be reduced, a reflected light-image produced by the light reflected from inside a living-tissue subject illuminated by an illuminating light, the fluorescent light image produced by the fluorescent light emitted by a living-tissue subject illuminated by a stimulating light, etc. can be observed as a light-image having a high S/N ratio.
In addition, if the photographing apparatus is a charge-amplification type photographing element that amplifies the charge by impact ionization, the readout noise is lowered, and the signal charge can be read out as an image signal having an even higher S/N ratio.